Bag house filter systems are well known in the art for removing particulate matter from gaseous streams. Often bag house filter systems are employed for removing particulates from air streams prior to exhausting the air to the atmosphere. Conventional bag house filter systems include a filter chamber having an inlet for receiving particle-laden air, a filtered air outlet, and a particulate matter discharge outlet. The filter chamber is generally partitioned so that the air stream is passed through a number of separate, air pervious filter bags mounted therein for entrainment of the particulate matter. Filter bags are typically of elongated tubular configuration mounted in parallel fashion within the filter chamber and supported by a plate which transversely partitions the filter chamber between the air inlet and the filter bags. Typically each filter bag has an open end that is fluidly connected to an opening in the support plate so as to receive a portion of the air stream flowing through the filter system, with the other end of the filter bag being closed. The filter bags are often supported internally by a tubular wire mesh structure.
In normal operation, a positive air pressure causes the air stream to flow through the porous tubular walls of the filter bags and out the outlet of the apparatus. The particulate matter is retained within the filter bags.
After a period of usage, particulate matter cakes on the inside walls of the filter bags and must be periodically removed to ensure efficient operation of the filter system. Conventional bag house systems include a cleaning mechanism for removing the caked particulate matter from the inside of the filter bags. Typically a cleaning head is swept across the open ends of the filter bags to clean them, either individually or in small groupings. The cleaning head is in fluid communication with a reverse air stream, and when aligned with the openings to one or more filter bags draws a suction through the filter bags. The suction causes the filter bags to collapse on the supporting wire frame and the caked particulate matter to fall from the filter bag walls, where it is ultimately discharged through the particulate matter discharge outlet. One such conventional bag house cleaning system is disclosed by U.S. Pat. No. 3,854,910 to Hammerquist, wherein the filter bags are arranged radially about a central axis of the filter chamber. The cleaning head is mounted on a sweep arm that sweeps radially around the filter chamber to sequentially pass over the opening of each filter bag.
Other conventional bag house configurations utilize air stream flows reversed for that described above. In such a configuration the contaminated air stream passes from the outside of the filter bags, through the filter bag walls, and exits through the open ends of the filter bags. The particulate matter cakes on the outside of the filter bags and is removed periodically by a continuously sweeping cleaning head that delivers compressed air to the openings of the filter bags to blow the particulate matter off the exterior walls.
Conventional bag house cleaning systems using suction type cleaning heads, such as that taught by Hammerquist, as well as those using compressed air cleaning, are limited in their efficiency due to the continual sweeping movement of the cleaning head. Since the cleaning head sweeps continually over the openings to the filter bags, it is only ever exactly aligned with the opening to any particular filter bag for an instant of time. Thus, each filter bag is only exposed to the full flow of the reverse cleaning air stream for that instant in time, with the remainder of the cleaning time being at a reduced air flow rate due to disalignment of the cleaning head with the opening for that particular filter bag.
One conventional solution to this problem is disclosed by U.S. Pat. No. 4,022,595 to Noland, which discloses an intermittent drive mechanism that radially advances a cleaning assembly stepwise around the circumference of the filter chamber. This results in a selected group of filter bags being in fluid communication with the reverse air stream for a finite period of time before the cleaning assembly advances to the next group of filter bags. However, the intermittent drive mechanism taught by Noland is exceedingly complex.
The Noland cleaning assembly utilizes a rotary blade blower mounted to continuously rotate about the axis of the bag house. The blower operates within a housing that is mounted to rotate independently of the blower. The housing has a transverse outlet to allow air from the blower to exit radially therefrom. Air exiting transversely from the blower urges the housing to rotate, with the air outlet revolving to sweep across groups of filter bag openings partitioned by plenums.
However, an additional mechanism of the Noland cleaning system prevents the housing from continuously rotating, causing it instead to rotate in stepwise fashion. That mechanism includes a circular plate that is mounted coaxially and above the blower housing. The circular plate is continuously rotatably driven by a motor. The underside of the plate includes a circular track formed thereon, with a stop plate cutting transversely across the track at one point. A four-legged crossbar is pinned to the top of the blower housing below the circular plate. A roller is pinned to the upper side of the end of each crossbar leg, each roller being insertable into the track formed on the bottom of the upper plate.
The crossbar leg opposite of the leg inserted into the track projects radially outward into one of the plenums opening to a group of filter bags. Each rotation of the circular plate causes the crossbar leg roller engaged in the track to hit the transverse stop plate, causing the crossbar to rotate by 45.degree.. Rotation of the crossbar results in a third leg of the crossbar being inserted into the next plenum and allows the blower housing to rotate incrementally to blow air into a subsequent grouping of air bags.
The intermittent drive taught by Noland does result in stepwise cleaning of groups of air bags. However, the complexity of the drive mechanism renders the drive costly and prone to increased maintenance and down time.